The association of neuromuscular disorders with thyroid dysfunction has long been recognized and extensively described. However, the role of thyroid hormone as a differentiating agent in promoting normal development of both neuronal and non-neuronal components of specific reflex pathways which must be mature at the moment of birth in order for the newborn to survive, has not been clearly understood. The objective of the proposed research is to provide correlative morphological and behavioral information about the role of thyroid hormone on maturational processes involving central (neuronal) and peripheral (non-neuronal) structure in the emergence of coordinated function. The relationship between hand and mouth activity provides a good model system for this study, since this relationship is established very early in ontogeny and is retained perinatally and postnatally, where they appear as the well known Palmomental and Babkin reflexes. The origin and sequential development of hand and mouth activity will be evaluated under (a) normal, and (b) experimental states, in which an antithyroid drug is fed to pregnant animals such that fetal and maternal thyroids are inhibited. This will be followed by studies of synaptic patterns at the light and EM levels of specific neuronal and non-neuronal structures. These data will be correlated with studies utilizing autoradiography following labelling with (3H) proline and leucine, and horseradish peroxidaxe (HRP) which is widely used as a tracer. These experimental approaches will be used to determine the role of thyroid hormone on developmental events involving neuronal components, which may underlie the emergence of coordinated function between hand and mouth activity. It is expected that information will be derived relative to the trophic role of the hormone, and will put us in a better position from which to consider, test and identify congenital and/or acquired myopathies, where hormonally associated abnormalities are the suspected basis of arrests of development.